Book Image

Amazon SimpleDB Developer Guide

Book Image

Amazon SimpleDB Developer Guide

Overview of this book

SimpleDB is a highly scalable, simple-to-use, and inexpensive database in the cloud from Amazon Web Services. But in order to use SimpleDB, you really have to change your mindset. This isn't a traditional relational database; in fact it's not relational at all. For developers who have experience working with relational databases, this may lead to misconceptions as to how SimpleDB works.This practical book aims to address your preconceptions on how SimpleDB will work for you. You will be quickly led through the differences between relational databases and SimpleDB, and the implications of using SimpleDB. Throughout this book, there is an emphasis on demonstrating key concepts with practical examples for Java, PHP, and Python developers.You will be introduced to this massively scalable schema-less key-value data store: what it is, how it works, and why it is such a game-changer. You will then explore the basic functionality offered by SimpleDB including querying, code samples, and a lot more. This book will help you deploy services outside the Amazon cloud and access them from any web host.You will see how SimpleDB gives you the freedom to focus on application development. As you work through this book you will be able to optimize the performance of your applications using parallel operations, caching with memcache, asynchronous operations, and more.
Table of Contents (16 chapters)
Amazon SimpleDB Developer Guide
Credits
Foreword
About the Authors
About the Reviewers
Preface

Eventual consistency


Simple DB can be thought of as a Write-Seldom-Read-Many model. Updates are done to a central database, but reads can be done from many read-only database slave servers.

SimpleDB keeps multiple copies of each domain. Whenever data is written or updated within a domain, first a success status code is returned to your application, and then all the different copies of the data are updated. The propagation of these changes to all of the nodes at all the storage locations might take some time, but eventually the data will become consistent across all the nodes.

SimpleDB provides this assurance only of eventual consistency for your data. This means that the data you retrieve from SimpleDB at any particular time may be slightly out of date. The main reason for this is that SimpleDB service is implemented as a distributed system, and all of the information is stored across multiple physical servers and potentially across multiple data centers in a completely redundant manner....